Posted
by
Soulskillon Thursday January 19, 2012 @11:14AM
from the apparently-you-can-stop-the-signal dept.

itwbennett writes "Would-be cellular carrier LightSquared claims that the company's LTE network was set up to fail in GPS interference tests. 'Makers of GPS (Global Positioning System) equipment put old and incomplete GPS receivers in the test so the results would show interference, under the cover of non-disclosure agreements that prevented the public and third parties from analyzing the process,' LightSquared executives said on a conference call with reporters Wednesday morning."

And thank god for that. Forget the millions of drivers for whom GPS is a convenience; LightSquared would spell an end to the major advanced in aviation navigation systems and the accompanying time- and fuel-efficiency gains that have come with it. Check out Canadaian airline WestJet's use of so-called "RNAV" approaches into airports; their use of GPS in those systems saves them millions of dollars in fuel every year, plus gives them and their passengers the benefit of faster trips. No more bouncing around through the 3000 or so VHF Omnidirectional Radio beacons that dot North America.

And thank god for that. Forget the millions of drivers for whom GPS is a convenience; LightSquared would spell an end to the major advanced in aviation navigation systems and the accompanying time- and fuel-efficiency gains that have come with it. Check out Canadaian airline WestJet's use of so-called "RNAV" approaches into airports; their use of GPS in those systems saves them millions of dollars in fuel every year, plus gives them and their passengers the benefit of faster trips. No more bouncing around through the 3000 or so VHF Omnidirectional Radio beacons that dot North America.

Actually, you mean RNP (Required Navigation Performance) which are a set of approaches that are more efficient, but require that the plane have onboard a minimum set of equipment. And one of this is dual RAIM [wikipedia.org]-locked GPS units.

A RAIM-locked GPS is a receiver that can see more than the 4 minimum GPS satellites - and all aviation GPSes have utilities that can take a location (destination) and time and calculate whether or not a RAIM lock is achievable (it depends heavily on the satellite configuration at that point in time).

Primary purpose of RAIM is to help the GPS decide if a satellite is "out of whack", which is essential if you need to figure out your position accurately.

RNAV is slightly different - it requires a flight management system that basically generates a GPS-like path by taking in multiple navigation sources like VORs and NDBs and calculating a virtual track based on your position relative to those navaids. So you're not flying navaid to navaid, you're flying a course through but using the navaids to cross-reference your position continually.

These days, a combination of RNAV, INS (Inertial navigation system) and GPS are used altogether to get very accurate positioning required for RNP. (RNP dictates the minimum performance your navigation equipment can have - you can always use better equipment to fly the RNP approaches more precisely).

It comes down to the fact that there is currently no way to reliably demodulate and decode a signal sitting down at -130 dBm (roughly the strength of a GPS signal in some areas) while you're experiencing interference trillions of time stronger as a result of sidebands from a base station.

It's a fundamental concept that all time limited signals mathematically have infinite bandwidth. However, the FCC defines bandwidth by the region where 99.99% of the power resides. Let's say you have a 150W base station. That would mean up to 1.5e-2W is outside the targetted frequency band. Now lets assume about.001% of that power resides on top of the band where your signal of interest is coming in. That would mean 1.5e-7W is on top of your signal of interest or (-38dBm). For reference, the signal at -130dBm is roughly equivalent to 1e-16W.

The numbers above are general estimates used for illustration, but lets say that only.0000001% of the base stations power falls into the band where your signal of interest resides. That interfering signal is still sitting at -68dBm while your GPS signal is sitting at -130dBm.

Nice calculations, but they ignore two facts: 1 - the LightSquared frequency is actually pretty far from the GPS frequency (10s of MHz), so the filtering challenge is not as bad as you make it out to be. 2 - Military spec GPS devices have no problems nor do they suffer reduced sensitivity, if someone is already doing it then it definitely can be done.

1 - the LightSquared frequency is actually pretty far from the GPS frequency (10s of MHz), so the filtering challenge is not as bad as you make it out to be.

I did not ignore this fact. As I stated, all time limited signals have mathematically infinite bandwidth. So it doesn't matter how far away on the spectrum one frequency is from another, some part of the signal from the frequency will spill into another.

For quick reference see this: http://en.wikipedia.org/wiki/Bandlimiting

When something like this happens, it's not just about filtering anymore. Filtering only gets rid of the unwanted sideband signals. However, if a larger signal happens to be sitting right

Yes, it can be done if you have a mil-spec budget to go with your mil-spec requirements. Do we really want personal GPS devices to cost thousands each?

There is a certain humor though in replacing the polite woman saying "you have missed your turn. Please make the next legal U turn" with "What is WRONG with you MAGGOT? Didn't your mamma teach you to pay attention? When I say TURN you will turn NOW! Drop and give me 50!"

Any receiver that does not directly sample the RF input employs a "superheterodyne" design with a local oscillator and a mixer to downconvert the desired signal to something that can be demodulated and processed. GPS frequencies are high enough that it's not practical (today) to directly sample them.

There is always some leakage of the local oscillator through the other mixer port. There may also be some leakage of the downconverted intermediate frequency (IF).

In my youth I made a "police detector" using this principle. It worked quite well.

GPS receivers are designed to filter out the neighboring frequencies, when the neighboring frequency sources are satellites transmitting at power levels comparable to GPS satellites.

That is how that portion of the spectrum was designed and allocated. LightSquared is trying to use terrestrial transmitters at these frequencies. GPS receivers were never designed to filter out their signal from neighboring sources that are literally a billion times more powerful.

You don't know anything about RF transmission and why there have always been transmission power restrictions on the allocated spectrum. The spectrum allocation was specifically designed to prevent this exact situation from occurring.

I can actually see LightSquared perspective. In an ideal world, the solution would be to fix all those devices that are affected by things they shouldn't be affected by. Just not likely to happen.

At the same time, they are using something slotted for satellite communication, so it's somewhat reasonable for GPS devices to not have been designed to filter something they never expected to be subjected to.

Your boss comes up to you and says "Make a GPS receiver". As part of your design, you know you'll need a filter to block signal that's out of the GPS band. So what do you do? Do you make the biggest, baddest filter that you can possibly achieve without regard for expenses?

Or do you analyze the expected power in nearby frequency bands to determine what kind of specification your filter must meet in order to work efficiently without driving up costs unnecessarily?

"Proper engineered devices" would be the ones with the engineer who knows he needs -x dB/octave roll-off in his filter because he knows that the signal in adjacent bands cannot legally exceed y dBm because of the way the FCC has allocated the spectrum. And it is those devices which will get fucked in the ass by Light Squared - all because some engineer actually did his homework.

Exactly. They took relatively cheap satellite spectrum (cheaper, because you have to put satellites in orbit) and tried to get it re-purposed as ground-based spectrum, which costs billions of dollars more. It was really pretty ballsy and elegant; make your spectrum worth billions of dollars more just by filing paperwork and hoping that you slip by.
The REAL kicker came in when DirectTV, and pretty much every single company that owns satellite spectrum said "what's good for the goose is good for the gander" and all filed paperwork requesting the same waivers. I mean, you can't expect them not to try and make the spectrum that they already own worth billions more. So, the FCC got flooded with all of these waivers, realized that this was going to destroy spectrum allocations across the US and cause untold disruptions as you open up massive chunks of bandwidth to high power, ground-based transmitters.
We're not talking about just knocking out GPS. If LightSquared got approved, they'd have to approve other companies waivers also, and but pretty much every single service that relies on a satellite would go kaput. Pretty simple decision for the FCC to make....

No, they bought a band that is designated for low power satellite communication and are trying to get the designation changed to allow high power terrestrial communication. They aren't an innocent bystander in this mess.

They are just completely fucked, and I actually feel kind of bad for them. I mean, they theoretically "own" this nice slice of wireless spectrum, which they bought at considerable expense, and they want to do something pretty cool with it, but they're not allowed to because some other industry has been illegally bleeding into their spectrum for years and now it's too late to fix it.

Here we go again... and again...and again. A grant to spectrum comes with fine print dictating how it can be used. You simply do not have the right to do whatever you want as long as it remains in-band..

Their existing allocation was provided under the ATC integrated services rule which explicitly prohibits proliferation of ground stations.

What they did was apply for an exemption to the rule they had purchased their spectrum under which has thus far not been granted due to interference concerns.

As I understand it, it's not so much bleeding as lack of filtering. Lack of filtering because the chunk of spectrum was slotted for low powered satellite to earch communication, not the high power they want to use it for.

They are trying to get permission to use it for a purpose it was never intended for, as part of that they have to prove that the change won't interfere with anything.. and of course.. it is interfering with stuff.

I really do feel for them.. it's a pretty shitty deal.. but it's not like they bought a chunk of land to build something and can't get rid of the squatters. It's like they bought a chunk of land in a residential area and are trying to put up a skyscraper.

Why do you feel for them? They bought something from the People and then turn around and say 'We know you said we are only supposed to use it this way, but we are gonna use it this way, problem?" They brought this on themselves.

And they got a steal on the residential parcel and if they can get it rezoned for the skyscraper it's worth 100X what they paid for it. This was nothing more than a gamble to try to get spectrum reallocated to ground prices. They paid almost nothing for spectrum that if it was ground based would be worth almost 6 billion (based on the last auction). The entire reason the spectrum is cheaper is that it costs $2billion minimum to put a satellite in orbit to use it.

Lightsquared is neither innocent nor deserving of sympathy. They were told multiple times the waiver they were given was for testing. It would be foolish of the FCC to not allow them a chance to prove they have developed filtering technology capable of working around the physics. When their testing showed their signal would destroy high precision GPS they had the gall to suggest that the billions of installed GPS receivers have to be replaced that's when they lost all sympathy from me. I have a feeling they've not only known from the begining that this would never work but that they thought they had the political muscle to move it through. Not only that but I don't believe they ever really intended to build a network, but their real intention was to get the spectrum usage switched then sell it 10X what they paid for it.

If Joe sells you an off road vehicle then you try to get it licensed to be street legal do not get pissed at Joe because it will not be allowed on the road.Radios are very complicated. Till I got my current job I had no idea how little I knew about them. Get education on the subject. They are attempting to use this spectrum in a way in which their current license specifically prohibits. Also it is prohibited for a very good reason. They are trying to change their license and it is that change that is causing the problems.

That makes sense, sounds like the "If this is the case..." that I started with is not the case.

I don't understand specifics on transmitted electromagnetic radiation, but I had assumed that the company was licensed a portion of the spectrum from x to y and were staying within that area. To me it seems like it should be a simple issue: if they're bleeding into other portions of the spectrum then they're violating the license, but if GPS had been poaching spectrum then it's at fault if someone wants to legiti

Do not need to.It really is simple.The Lic that they got was for a specific spectrum to be used for low power transmissions from satellites.That was what they were sold. GPS Satellites use a similar low power part of the spectrum.LightSquared wants to put the transmitters on the ground at a much higher power. The effect is that GPS receivers are now left trying to filter out "noise" that is many orders of magnitude stronger than the signal itself. This is bad.

It is a real world test. LightSquared has this fantasy that people replace GPS hardware like they do cell phones every two years (or less). There are LOTS of GPS receivers out there that are 10+ years old, and they can't grasp the fact that THOSE WORK FINE.

See my other comments on the GPS 12 for an example. Similarly, there are *tens of thousands* of GNS 430\530 GPS\NAV\COM units in aircraft around the world, and those had a time on market of over a decade. They'll have support for years to come as well. At $15-20k each, people aren't going to run out to replace them.

From what I gather from that article.. Many GPS devices are "operating" outside their spectrum as well -- They scan frequencies just above and blow their spectrum to help 'filter' and find the signals they want... This means cell towers operating within their proper frequency would screw up GPS receivers that need that out-of-band data to help filter

Since the bands above and below are also reserved for satellite downlinks, by definition, no cell tower operating there is within it's proper frequency. LightSquared bought a chunk of that spectrum knowing that was the case and is now petitioning to have it re-designated. The FCC reasonably offered them a chance to show that their request for a change after the fact wouldn't harm existing communications. The tests didn't prove out.

GPS manufacturers made their decisions on the strength of promises they got f

Not really. He portrays it as some kind of heroic battle between some Goliath GPS industry and their army of lobbyists and the poor innocent LightSquared, failing to mention their billions of dollars of backing, or the fact that their own lobbyists were probably the only reason they managed to push this through despite the obvious technical flaws and all the rules designed to prevent exactly the kind of interference they will cause.

In the same manner of speaking maybe testing it around charged multi watt coils should be on the board. If the receivers were out of spec and not actually FCC compliant then you couldn't really fault the carrier. It would be the same as Bell having to work around me mucking around with some electrical equipment and broadcasting on their channel.

If they want it to be a reasonable test of the systems capabilities you have to test against all parts of the spectrum equally. If indeed tests against faulty

Also, using an initial terrestrial based concept and moving it to satellite based doesn't transfer well when the power and noise thresholds differ by several orders of magnitudes from the former.

/quote>

That's a little backwards. It was an initial satellite based system (with terrestrial fill-in) and LightSquared desires to offer terrestrial only devices. Having terrestrial-only means there needs to be a greater number of towers ( or higher power towers ) to offer coverage.

The waiver issued a year ago was conditional. It was conditioned on not interfering

If this is fraud on the GPS companies' part or the testing authority's part then there should be hell to pay.

If this is sour grapes then LightSquared just libeled the companies involved.

If, on the other hand, "old and incomplete equipment" tests were a required part of the test for good reason, then LightSquared is a bit late in its complaints - it should've made these complaints well before testing happened, and its current statement should've started off with "As we said before the tests were run, testing for old and incomplete equipment is not a valid test...."

So ASSUMING Lightsquared, operating 100% within their spectrum, and not interfering with GPS frequencies, could still interfere with GPS because the GPS Unit itself is using part of Lightsquared's spectrum for filtering purposes.

They can't filter out LightSquared's signal. It'd be the metaphorical equivalent of trying to spot a candle flame standing next to a searchlight. It's just not physically practical. Worse still, LightSquared managed to get their spectrum at a huge discount exactly because it was technically unsuitable for the purpose they're trying to use it for now and the rules forbade that use - and then somehow managed to lobby the FCC into ignoring the technical side of things and let them go ahead anyway.

They used political muscle to get a testing waiver (personally I don't see anything wrong with allowing them to prove it doesn't work). The testing waiver doesn't give them the go ahead, it gives them permission to conduct testing and IF the testing reveals no interference or a path to eliminate the interference and IF the FCC concurs that this meets the minimum requirements of the law and IF no one else detects problems they might get a full waiver to proceed.

They didn't make it past the first IF and the military has already mobilized along with the very powerful farming interests which pretty much guarantee that regardless of their pull with the Obama administration the FCC cant' approve this. This thing would pretty much invalidate every single GPS produced before 2008 and most of the ones produced and built right up until this moment. That means the FAA suddenly doesn't have reliable navigation, the coast guard, millitary, surveyors, farmers and others can't know with precisions where they are (and most of these are critical aspects of the america economy). If the FCC allowed this forward they would get sued by every single player in the GPS world, that's not even including the fact that the military could just designate the towers as official GPS jamming systems and drop bombs on them.

Of course there's a good reason. Do you really think every GPS device out there is nearly new? There are hundreds of thousands of older devices out there still in use. It would be wrong NOT to test in such a way as to assure that these currently functional devices, which people payed their hard earned money for, continue to work properly.

The autohelm navigation GPS in my boat is 12+ years old and works fine. IT actually steers the boat to keep it on course. Unless the morons at that company want to buy me a complete new Autohelm system to solve the issue.

It doesn't matter what sort of equipment was used or what claims Lightsquared is making. It comes down to the simple fact that there is currently no way to reliably demodulate and decode a signal sitting down at -130 dBm while you're experiencing interference trillions of time stronger as a result of sidebands from a base station.

It's a fundamental concept that all time limited signals mathematically have infinite bandwidth. However, the FCC defines bandwidth by the region where 99.99% of the power resides. Let's say you have a 150W base station. That would mean up to 1.5e-2W is outside the targetted frequency band. Now lets assume about.001% of that power resides on top of the band where your signal of interest is coming in. That would mean 1.5e-7W is on top of your signal of interest or (-38dBm). For reference, the signal at -130dBm is roughly equivalent to 1e-16W.

Disclaimer: The numbers above are general estimates used for illustration purposes. Actual conditions may vary, but it is unlikely that they will vary in such a way that will let you reliably recover your signal of interest.Your -130dBm signal is

Garmin GPS-12 13(?) years old.Nagivo 3100, closing on 4 years old.In addition, many GPS receivers in general aviation aircraft are _significantly_ more expensive than domestic units, and are not replaced merely because the battery wears out.

You might be surprised how many GPS 12s are out in the wild. They (and their derivative devices for Marine and Aviation) are darn near indestructible. I have a GPS 12, I use it when I need to measure distances outdoors. Then again, I also have a GPSMAP 696, GPSMAP 740, GPSMAP 175, GPSMAP 195, GPSMAP 295, Streetpilot Colormap, iQue 3600, iQue m5, Streetpilot c330, Forerunner 310XT, and GPS 72, and that's all on one shelf. Yeah, guess what I do...

My first GPS was a GPS 12 I got on sale at West Marine. Ordered up connector kits from canada and made a wall wart/DB9 cable and a 12V/palmpilot cable. Still have it, still works great. It takes slightly longer to acquire than some units but if you set it down with a clear view it's usually pretty good.

The only quibble I have is that I would have had to pay more for an external antenna jack. For what it is, it's a gem - back then the interface was actually quite good:) I also remember being really impressed with the connector, which was built to last. My modern navigation-type GPSes keep killing power connectors.

I have a GPS 12, I use it when I need to measure distances outdoors. Then again, I also have a GPSMAP 696, GPSMAP 740, GPSMAP 175, GPSMAP 195, GPSMAP 295, Streetpilot Colormap, iQue 3600, iQue m5, Streetpilot c330, Forerunner 310XT, and GPS 72

It sounds like you could have provided all of the test units for this experiment.

1. I have an Edge 705 with the latest firmware (3.30 I think) There are a couple of outstanding problems with this firmware, specifically relating to interaction with my CycleOps power meter. First, it auto-calculates wheel size to a ridiculous 1500mm (should be on the order of 2100mm). Secondly, it generates occasional spurious auto-pauses even though the bike is in full motion. And thirdly, the cadence signal is highly erratic. This may or may not be related to my owning an early 705 that I th

1. I don't know much about the Edge devices. It may need its memory wiped if any erroneous garbage has accumulated there; its possible for a device to get into a weird state where things simply don't work right for no obvious reason. I think you power it down, hold the bottom two buttons down, press the power button once while still holding the bottom two buttons down, then let go when the Garmin logo disappears. My Edge 800 had issues that this fixed. Don't quote me on that. I don't know how much effo

What possible motive do the GPS manufacturers have for rigging the tests? If modern, properly-configured GPS units don't recieve interference, then why would they care? I read the article expecting some important link, like Garmin having an alliance with Verizon, but there was no mention of that.

In fact if anything, GPS makers would enjoy selling modern units to customers with older units that no longer work because of LightSquared.

Sorry, but it's just too much of a stretch to believe in this conspiracy. I think LightSquared are simply desperate to get the FTC to give them their waiver. Their business is royally screwed without it.

A lot of aircraft GPS receivers are quite old. It can cost 10-20K$ to put a certified receiver in a light aircraft, so pilots will keep their existing equipment as long as possible. Changing the requirements on interference resistance might require very expensive re-certifications of these receivers.

And that's for a retrofit. What does one do (if something must be done) about units like a Garmin G1000 or the Avidyne units that have been installed in Cirrus planes for years? Factory-installed units intended to be core to aircraft operations are even more expensive than that.

Parent post is quite correct. The largest cost of a GPS receiver in an aircraft is NOT the electronics itself, but the installation and certification process, not to mention the database updates.

Remember that it has to work with many other transmitters and receivers nearby, including a Mode C or Mode S radar transponder required for most metropolitan regions, a UHF (403 MHz) ELT, a pair of VHF transmitters, possibly an HF SSB radio or an old DME system, and maybe even a weather radar. --and that's just the stuff that is supposed to deliberately transmit. Receivers can radiate their local oscillators...

The bottom line is that when you put safety of flight navigation equipment in an aircraft, it has to be tested and certified before it can be used. Lightsquared would like us to just "replace it" with something new.

I'd like to put their executives in an airliner filled with their damned LTE phones landing on a CAT III approach on a dark and stormy night. We'll see how "rigged" those tests were.

Let's say Lightspeed goes through. You now have another competitor for 4G LTE service (which is a good thing, right?) in places where there isn't great service (I assume part of the reason for the Government to consider this is "rural broadband.") potentially benefitting millions of people.

And the cost is that some guys who own their own airplanes might have to buy new GPS receivers?

If they were smart, they would tell Lightsquared back to the satellite with you. You made your bed, now lie in it. Oh and if you dont actually use the spectrum in the way you were licensed soon, we'll take it back with no refund.

So LTE needs a federal license which requires proof that their network transmissions do not interfere with GPS receivers. Well, lets see, apparently the GPS equipment worked when the LTE network wasn't on and when it was turned on the GPS had issues. So what LTE is saying is that everyone with old GPS receives has to upgrade them because their network causes issues with them so that they can get a FCC license in order for their network to be deployed everywhere. Are they assuming that people buy all new electronics every year? I mean especially testing this on a military base, when I was in the military I used computers that were designed before I was born. I have a 30 year old television myself, if LTE decides to make a network that stops my television from working isn't that their problem. The whole purpose of the FCC license is to ensure that someone doesn't put new equipment into use that will stop the use of old equipment. Okay, maybe not the only purpose, but that one is at least important.

So LTE's network failed in real world conditions and they are blaming GPS manufactures for that failure. I don't think they have a case because the GPS manufactures likely did not go back in time and put in circuits to stop their equipment from running if they detected LTE's network. It's probably a good thing it wasn't raining either or they would have to sue God for conspiring against them.

You've got it all a bit twisted. There's no entity called "LTE". The company is LiqhtSquared ( name is in the article title ) LTE stands for "Long Term Evolution" and refers to one of the newer mobile phone/data schemes.

deliberately chose obsolete and niche GPS devices that would show the most interference... The tests also included receivers that were tested without interference filters that normally would be included in a complete device for consumers

If true, the use of units without filters may be enough to invalidate the tests. It would be similar to testing a microwave for radiation leakage, with the door removed.

1) GPS manufacturers are not a direct competitor to a wireless networking company. If Verizon or AT&T were complaining they might have a case.2) GPS was there first.3) Clearly the Lightsquared hardware is spitting out a harmonic which could be fixed but would probably make the devices much more expensive to produce.4) Lightsquared has been trying this case in the court of public opinion by running full page newspaper ads instead of dealing with the technology issues.5) Lightsquared has been making huge political donations and receiving government grant funding which makes the whole thing stink like old fish.

3- Sometimes you can get harmonics of the base clock frequency that sneak their way into the mixer and end up in the RF range. For example, if they were using a 14 MHz clock, its third harmonic would be 42 MHz, which could then get upconverted to 1572 and interfere with GPS. I don't actually know if that's the case (they could be using direct modulation for all I know, in which case they wouldn't even have this problem), but it is possible.

All I can say to LightSquared is... (sarcasm on) "Right...." (off)
This company is *done* unless they can find a way to lower their required power or move their spectrum away from GPS. They are fighting for their very existence and it's getting down to the wire so they are saying *anything* in an attempt to keep things going. The test was rigged eh? Guess physics did you in guys, no need to rig the test.
Had you asked an RF engineer you could have saved yourself a pile of cash trying to fight this issue. If the FAA didn't do this idea in because it would make Airborne navigation using GPS unreliable (and thus end the practice), the DOD's arguments should win the day. Further, the FACT that the consumer use of GPS would surely be impacted (if not totally disabled) for miles around their transmitters regardless of what they do should nail the coffin shut.
I guess, to be fair, with the FCC buying tickets to the Broadband over Power Lines (BPL) circus, the chance that they'd buy into this sideshow was worth a try. However, the game is over guys.

LS is full of it. I used to do testing of this nature for the Navy. I know many of the people who would have done this testing for the USAF. Never in 6 years of working in that field did we ever require a contractor who had submitted equipment for test to do so with no knowledge of what the test would be. They are blowing smoke to cover their asses in the hope that "the right people" won't know any better.

However the claim is that the Lsquared signals are a "billion times greater in strength" than GPS, and I know my modern GPS unit seems to have trouble locking on at times.http://www.insidegnss.com/node/2498 [insidegnss.com]

For surveyors, GPS basestations + roamers used for surveying are in the $10,000+ dollar range, and you don't replace them every few years.There's always going to be significant amounts of "old" (and old in terms of the 2-year churn for mobile phones) GPS equipment being used by the folks who need extremely high levels of accuracy.

it's not about filters, nor is it about "GPS listens outside its band"

GPS receivers have "wide open" front ends and always have for good engineering reasons:1) Spectrum planning ensured that there's no high power signals in adjacent bands (i.e. the adjacent band is also for satellite signals)2) "brick wall" filters are heavy, expensive, large, and have bad effects on the inband signals (see, e.g. any digital audio application since CDs started being sold 30 years ago). Your cellphone has GPS that is as small as it is partly because you can use a fairly wide open front end that doesn't require a lot of filtering.3) GPS signals are below the noise floor, allowing use of 1 bit ADCs in receivers, reducing cost and complexity in receivers.

There's quite a bit of arguing about what is an appropriate propagation model from L2 terrestrial transmitter to GPS victim. L2 would like to use a conventional communication model. GPS folks would like to use a jammer/interference model. The difference isn't in the "mean power" but is in where the outliers are. For comm, your concern is that your worst case low power deviation is still high enough that you can "close the link" (i.e. not drop the call). For interference, your concern is that the worst case high power deviation is still low enough that it doesn't interfere with your link. The problem is that in urban environments, the distribution isn't uniform and is highly skewed (lots of reflecting surfaces and multipath.. distance isn't as big a factor as just the number of bounces). There's lots of deviations below the mean, but small ones, and relatively few deviations above the mean, but they are huge (e.g. "hot spots"). We're talking 15-20 dB difference between the 5% low end and the 5% high end

There's also arguing about what "performance degradation" is acceptable. L2 would like to claim that 6-8 dB is ok, while GPS industry would like to use 1dB. That's because communications uses error correcting codes and such, and can tolerate dropouts and degradation. GPS is more like radar, and relies on measuring the timing of the signal, and doesn't have as much in the way of error correction or error tolerance, so they've historically used the radar standard of 1dB degradation. The GPS industry is a bit stretching here, because with new receiver designs (which might consume more power and be bigger) they could probably deal with the worse interference environment. But that's a 10-20 year kind of project.

So the tests were fair, with published test criteria, and only now, a week from their deal with Sprint expiring (after a 30 day reprieve) they're starting to raise these questions.

Missing from the discussion is why this happened to begin with. The Federal Communications Commission was created with the explicit mission to avoid allocation problems like this with the electromagnetic spectrum. This is not the first time they've screwed up like this. In the late 1980s we installed a SCADA sytem on 928.8 MHz. A year after we were up and running, high power paging showed up on 929.03 MHz. You could light a neon bulb with the energy we were getting from our Master receiver antenna.

Our remotes were transmitting with 5 watts and the paging systems were transmitting with over 3 kW ERP. Our receivers had been optimized for sensitivity, not selectivity. But even with the state of the art receivers designed for selectivity, we were still getting clobbered. Only with massive effort did we overcome this problem.

The FCC screwed up because they don't do their homework any more. Even back then, engineers were being relegated to the broom closet while attorneys and political hacks took charge. Applicants were being told to hire consultants to suggest available frequencies, do interference studies and to submit the consultant's work with their license application. Tell me there wasn't a conflict of interest even then!

For all I know things are still like that today. LS probably paid for a consultant who told them what they and the FCC commissioners wanted to hear.

This is why we can't have nice things. We need an FCC to keep this from happening. And instead of an FCC, we get political hacks of both flavors who don't know a damned thing about the state of the art or even what the radio spectrum is.

While I'm sympathetic to your situation... did you have a FCC license for your SCADA system? If you didn't, that sucks but there's not really anything to complain about. But I'm assuming you did, in which case they should've asked you, and any other potentially-interefered parties. If they didn't ask, you probably had grounds for a lawsuit.

An unpleasant situation that never should've happened... but it's hard to imagine a situation in which you had no recourse.

They bought spectrum that was cheap because it was designated for satellite to ground transmission, then they demanded it be redesignated for ground transmission

they have no claim against the FCC, what they did would be like buying up some cheap land that was zoned to be used for parks/rec centers then whining that they cannot open a nitroglycerin factory next to the city park

Hmm. So, their equipment is generating interference with GPS receivers, and Light Squared is blaming the implementation of those receivers as being non-standard, and subject to interference that a properly implemented GPS receiver would not? And everyone is claiming that Light Squared is full of bullshit?

Interesting. I've heard of the name of the company once before (probably from an article on Reuters), but when I performed a search at the time, I couldn't figure out what they were doing that was worth all

Haha. If what you are saying is true, given the current way politics has been leaning, they may have had a chance if it only affected the civilian market; however, since it affects the military as well, I imagine the DoD giving up on that portion of the spectrum only after the United States has been dissolved as a country.

Still, I would be quietly entertained if they did somehow manage to get that spectrum away from the DoD. The amount of screaming you'd hear on C-Span from various generals testifying befor